Sedimentary Characteristics And Tectono-paleogeographic Implications Of The Yongning Formation In The Liaodong Peninsula,China

The Liaodong peninsula is located in the northeastern part of the North China continent,characterized by extensive development of the Neoproterozoic continental margin basins,and it is a key area to study stratigraphic sequence,sedimentary geological characteristics and tectonic palaeogeography pattern of eastern North China and Northeast Asia in later period of late Precambrian.The Yongning formation is mainly exposed to the middle of the Liaodong Peninsula,laied on the early Precambrian metamorphic basement with angular unconformity and conformably covered by the Xihe group.Using theories and methods of chronology,sedimentology and geochemistry,this paper investigated the stratigraphy,sedimentary geology and tectonic palaeogeography of Yongning formation and further analyzed the prototype basin and plate tectonic background of Yongning formation through regional comparative study.The main new understandings are as follows.1)Tt is the first time to obtain that the minimum peak age of detrital zircon is1213.6 + 8.6Ma in the lower argillaceous siltstone of the lower Yongning formation,which means the age limit of Yongning group is more than 1213.6 + 8.6Ma,similared with Zhixian group in the Pingnan Basin of Korean Peninsula,Fuzikang group in the Changdao Countyof Shandong Province,Tongjiazhuanggroup in the Yishui County of Shandong Province.2)Based on the deep study on sequence stratigraphy,sedimentary facies and sedimentary facies sequence of Yongning formation,it is confirmed that the main body of the Yongning formation is fluvial facies,and is generally composed of water advance and retreat series.3)Graphic display of 198 sets of troughs and wedge-shaped large diagonal beddings in the field showed that the ancient flow direction was from north to south,and the provenance area is located in the south of the Yongning formation outcrop area.4)The statistical results of sandstone skeleton particles and the geochemical characteristics of sandstone indicate that the source area of Yongning formation is mainly stable cratonic or uplifted basement,followed by the orogenic belt of re gyratory.The tectonic position The tectonic location of provenance was mainly the active continental margin,followed by the passive continental margin.This result,combined with the age of detrital zircons,indicate that the sediments of the Yongning Formation mainly originate from the Paleoproterozoic granitic rocks within the orogenic belt and the metamorphic basement of ancient continental blocks on both sides.Based on the analysis of the geochemical characteristics of Yongning formation and the comparative study of the volcanic rocks in the Yongning formation,it is considered that the main body of Yongning formation is the continental depression controlled by continental rift system.